As a container formed of resin, there is known a PET bottle having a configuration disclosed in Patent Document 1 for instance. In this, there are disclosed a constricted portion and a rib which are elastically deformable to absorb a load when such load is applied vertically to the PET bottle, thus preventing collapse of the PET bottle.
On the other hand, in the market, there have been developed resin containers of various shapes in accordance with e.g. customer's tastes, which are divided mainly into cylindrical containers having a circular cross-sectional shape and square-column shaped containers having an approximately square cross-sectional shape.